Comparison of Turbine Tip Leakage Flow for Flat Tip and Squealer Tip Geometries at High-Speed Conditions

Abstract

The tip leakage flow characteristics for flat and squealer turbine tip geometries are studied in the von Karman Institute Isentropic Light Piston Compression Tube facility, CT-2, at different Reynolds and Mach number conditions for a fixed value of the tip gap in a nonrotating, linear cascade arrangement. To the best knowledge of the authors, these are among the very few high-speed tip flow data for the flat tip and squealer tip geometries. Oil flow visualizations and static pressure measurements on the blade tip, blade surface, and corresponding endwall provide insight to the structure of the two different tip flows. Aerodynamic losses are measured for the different tip arrangements, also. The squealer tip provides a significant decrease in velocity through the tip gap with respect to the flat tip blade. For the flat tip, an increase in Reynolds number causes an increase in tip velocity levels, but the squealer tip is relatively insensitive to changes in Reynolds number.

Squealer Geometry Effects on Aerothermal Performance of Tip-Leakage Flow of Cavity Tips

“…Both the cavity tip and the suction-side squealer tip performed better than the flat tip. Cavity tips were also found to produce lower loss than the flat tip in a number of other studies: e.g., Key and Arts [3] and Zhou and Hodson [4]. In terms of mechanical design, the centrifugal loading of a blade with a cavity tip is lower than that of a flat tip, so cavity tips are also preferred from this point of view.…”

“…So less of the chord is choked over the cavity tip than over the flat tip. Key and Arts [24] studied the tip-leakage flow characteristics of a flat tip and a cavity tip in a high-speed linear cascade. The cavity tip reduced the leakage flow more effectively than the flat tip.…”

Effects of endwall motion on thermal performance of cavity tips with different squealer width and height

“…Cavity tips were found to produce lower loss than the flat tip in a number of other studies, e.g. Key and Arts [4] and Zhou and Hodson [5]. In terms of mechanical design, the centrifugal loading of a blade with a cavity tip is lower than that of a flat tip, so cavity tips are also preferred from this point of view.…”

Tip leakage aerodynamics over the cavity squealer tip equipped with full coverage winglets in a turbine cascade

“…In a rotating turbine facility, Camci et al (2005) showed that suction-side partial squealers are aerodynamically superior to pressure-side partial ones and channel arrangements. Key and Arts (2006) found at high speed conditions that the cavity squealer tip provides a significant decrease in velocity through the tip gap for h/s = 1.34%. Lee and Chae (2008) studied the effect of cavity squealer rim height (h st ) on the aerodynamic losses in a turbine cascade for h/s = 1.36%.…”